Composite body and method of producing the same



Patented oct. 29, 1929 V V UNITED STATES JOHN WESLEY MARDEN AN D HARVEYCLAYTON RENTSCHLER, OF EAST ORANGE, NEW JERSEY, ASSIGNORS TOWESTINGHOUSE LAMP -COMP. ANY, A. CORPORATION OF PENNSYLVANIA COMPOSITEBODY AND METHOD OF PRODUCING THE SAME No Drawing.

a process for the production of composite posite bodies geneousmaterial,

bodies of refractory metals and to the articles produced thereby.

It is necessary or advantageous in many arts to employ, in lieu of asingle homocomposite bodies consisting of consolidated materials havingdiffer.- ent properties. Conditions making such comdesirable arise, forinstance, when a small amount of comparatively expensive material, usedin combination with a cheaper material, will serve the same purpose'as abody or article consisting entirely of the former. As an example of suchcombination, the coating of a common metal with platinum for use aselectrodes in the electro chemical arts may be cited. x

Other circumstances requiring a composite body arise when a materialhaving valuable properties can, only with difiiculty, be fabricated sinly to adapt it for practical use but may be more readily worked as oneof the elements ofa combination. An example of such character is presentwhen it is desired to utilize metallic thorium as electron-emissonmaterial .in'electrical devices, such as vacuum tubes used in wirelessapparatus, hot-cathode rectifiers of the Rectigon type and X-ray tubes,all of which require a heated filament and preferably one having highelectron emissivity at temperatures not incompatible with a long-burninglife. For such purposes, the thorium should be drawn into wire form toadapt it; to be heated by the electric current. It has beenfound-possible by employing the process hereinafter described, toreadily produce a composite wire comprising a base material, such asmolybdenum. coated with thorium. which, as electron-emission material,is as valuable as a wire consisting entirely of -metallic thorium.

In other circumstances a composite body is superior to a homogeneousbody. For example, an X-ray target at which X-rays are generatedpreferably consists of a refractory metal of high atomic Weight andanother metal of high heat-dissipating capacity, the

Applicatioii filed August 1, 1921. Serial No. 489,108.

former being necessary for the generation of powerful X-rays and thelatter so that the heat generated by electronic bombardment of thetarget may be dissipated rapidly enough to prevent the temperature fromrising to the melting point of the material of which the target iscomposed. Such composite tar et may consist of a metal of high atomicweig t, such as thorium, consolidated with a body having a highheat-dissipating capacity, such as copper, chromium or other metal. Thecomposite bodies for such purposes may be very conveniently prepared bythe process of the present invention. It is, therefore, an object of thepresent invention to provide a process for the production of compositebodies and, more particularly, for the production of such bodiesconsisting of at least one refractory metal.

Another object of our present invention is the provision of a compositebody consisting, at least in part, of a metalof high electronemissivity.

A further object of the invention is the pro-- vision of compositebodies which shall be valuable in increasing the efliciency and theburning life of electric devices, such as incandescent electric lampsand the like.

Other objects of the present invention will be apparent from a readingof.the following specification.

In order to secure the advantages of composite bodies, well-knownmethods such as rolling, drawing and electrolytic deposition have beenemployed. These methods have often been successful when the materials tobe united were malleable, ductile, or did not easily combine chemicallywith other elements. When, however, the materials sought to be combineddid not possess the requisite properties for such methods offabrication, combinations of certain materials having valuableproperties were not available. For example, the combination of anon-ductile metal, such as zirconium, could notbe drawn in connectionwith another material as a base. Up to the present time it has beenfound successful attempt was made to coat a tungsten wire with thoriumby surrounding the former with a quantity of thorium powder. The twometals, in contact, were heated in a high vacuum to a temperature whichwould 'be" thought suflicient to cause a union of the two metals. Theresultant product, however, when tested for electron emissivity did notgive results characteristic of thorium, showing that, if a smallquantity of the latter metal did adhere to the tungsten, it veryprobably was left in such physical condition that it was quicklyoxidized when exposed to the air.

Other experiments conducted by us have shownthat compounds of certainmetals cannot be made to form a composite body with another material byapplying a compound of the metal to another material as a base,attempting to reduce the metallic compound and subjecting the materialsto a heat treatment with a view to effecting a union between the reducedmetal and the base material.

That part of our present invention which relates to the method ofproducing composite bodies is particularly valuable for the utilizationof those metals which have such a strong chemical. afiinity for otherelements that they should preferably be Worked, in combination withanother material, in a very high vacuum in order to obtain them inadense, coherent and adherent mass. and it is still more valuable whendealing with such metals having a hi h melting point and also incombining with other. material metals which, in addition to possessing astrong chemical affinity and a refractory nature,

1 are also diflicultly. workable by such proc-' plies a verysatisfactory methodof produc"-' ing composite bodies, utilizing one ormore of suchmetals.

We have also utilized the present invention for producing compositebodies of refractory materials suitable for use as filaments inincandescent lamps. In this case. a base material may be coated by anysuitable method with a metal or mixture of metals or alloys havingdesirable properties such, for example, as selective light emissivity.

Another part'of ourinvention' consists in the discovery that metalshaving certain properties are valuable as agents for purifying othermaterials and for removing or converting from the active phase,materials which act deleteriously under certain circumstances, such asgases or vapors in vacuum and gas filled tubes which employ anincanlamp. such metals are especially valuable in removing deleteriousgases, such as oxygen, and vapors, such as that of Water, which quicklydamageincandescent bodies. Water vapor is particularly injurious,inasmuch as the interaction between water vapor and the incandescentfilament is a cyclic process, the

When employed in electrical first step in which is the decomposition of?1 the water vapor by the filament, resulting in the formation of ametallic oxide and free hydrogen. The oxides pf many metals, beingvolatile at the high temperature at which the filament operated, arethereby vaporized and are subsequently reduced by the hydrogen toproduce the original quantity of water vapor and the metal of which thefilament consists. The water vapor, being thus renewed again reacts withthe incandescent filament, and the. cycle described is continuouslyrepeated until the filament burns out.

It will thus be seen that, in order to eliminate water vapor and harmfulgases from such devices, metals such as zirconium, thorium, uranium,titanium, chromium, metals of the .rare earths, aluminum and magnesiumor a combination of two or more of the same, which react with them toform stable compounds therewith and especially those which formcompounds not reducible by hydrogen, are efiective in maintaining theefiiciency and prolonging the burning life of such devices. In thelamp-making art, materials which perform such functions are knownasclean-up agents and hereinafter.

will be referred to as such in referring to incandescent lamps andsimilar devices.

3 Various methods may be employed for introducingmetallic. clean-upagents into incandescent lamps and similar devices but a.

very convenient method is found to be the placement of theclean-'up'agent on the filament to form 'a composite body. Preferably,

after the lamp has been exhausted and sealed to the atmosphere, thefilament is then, for the 'first time, lighted .to incandescence and theclean-up agent is thus activated, that is, made to combine with theresidual gases and vapors. Part of the clean-up agent may be ing,

Up to the present time, we have found it best for producing compositebodies consistfor example, of two materials, to have one of them in theform of particles or in a pulverulent condition, While the material withwhich it is to be consolidated, may or may not be a dense, coherentmass. The material in comminuted form gives best results if it is placedin a medium or vehicle which is preferably a liquid or at least is in aplastic state. The material placed in the vehicle may, in some cases, bedissolved in the latter while, in other instances, the vehicle should beof such nature that it will not dissolve the added material but merelyhold it in suspension without reacting chemically therewith. Thematerial added to the vehicle should be thoroughly distributedthroughout the latter to obtain a homogeneous mixture. This mixture, inany desired concentration, is then applied to a material or body of anysuitable nature, form or size, with which it .is desired to unite theadded material to produce a composite body. The combination thusobtained is then treated by any suitable means, such as mechanicalworking or by heating, to cause the applied material to permanentlyadhere to the other body and iii to cause the particles of the appliedmaterial to form a permanently coherent body. During this step in theprocess, the vehicle should in most cases, be removed but, in otherconceivable conditions, it may not be necessary to do so. In dealingwith many materials it is necessary to give this treatment in an inertenvironment to avoid a change in the nature of the materials dealt with.In some cases, the atmosphere in contact with the materials employed maybe an inert gas while the treatment of other materials requires theoperations to be carried out in a vacuum and in still other instances anexceedingly high vacuum such, for example, as that obtained in ahigh-vacuum X-ray tube will give the best results.

Since it has been stated that one of the objectsof this invention is theprovision of a process for producing a composite body consisting, inpart at least, of a metal of comparately high electron emissivity, itwill be shown in suiiicient detail how such a body may be produced.Thorium will be selected as a metal representative of the class ofmetals possessing and also as a member of the group of refractorymetals. It is, moreover, a representative of that class of metals whoseoxides are not reducible by hydrogen and of which'c lass zirconium,uranium, beryllium, etc. are also members. Such metals, we have found,are particularly advantageous for increasing the efiiciency andmaintaining the candle power high electron emissivityofincandescentelectric lamps, as explained above.

Molybdenum will be assumed as the base material to which the thorium isto be united. Thorium, in a powdered eondition and in any desiredquantity, may be mixed with a vehicle consisting of a solution of nitrocellulose in amyl acetate until a homogeneous mixture results. Thismixture is then applied to a body of molybdenum which may, for example,be of wire form, by passing the molybdenum wire through the mixture. Thequantity of thorium deposited on the wire will obviously depend on suchfactors as the concentration of thorium in the mixture, the rate atwhich the wire is passed through it, and the nature of the vehicle.

The coated wire is then preferably placed inan air-tight vessel andconnected therein to electrical conducting terminals sealed into thevessel. The latter is subsequently exhausted to a very high degree ofvacuum by means of a pump which is preferably of the diffusion type.While maintaining the high vacuum in the vessel, electric current ispassedthrough the coated wire which is thus heated to a temperaturesufficiently high to remove the vehicle by volatilization and to causethe particles of thorium to be agglomerated and form a dense, coherentmass permanently adherent to the molybdenum base. The electric currentpassing through the wire is then cut out and the wire is allowed to coolbefore it is withdrawn from the vessel.

It is to be understood that the composite bodies produced according tothe present invention may consist of two or more consolidated materialsand that each component part may consist of mixtures or alloys. Forexample, a mixture of powdered thorium and powdered aluminum may beapplied to a wire of molybdenum or tungsten, and the aluminum will thenserve as a clean-up agent, preserving the thorium unoxidized to act asan electron emitter. Other variations in the products and process ofthis invention will be apparent to those skilled in the art but wedesire it to be understood that such are part of our invention as setforth in the appended claims.

What is claimed is:

1. A composite refractory metal body, com prising molybdenum as a baseand thorium consolidated therewith, said thorium having been firstapplied thereto as a suspension in a binder liquid and subsequentlypermanently consolidated thereto by heat in an inert environment.

2. A composite body comprising a base of molybdenum having thoriumconsolidated thereto, said thorium having been first applied to saidbase as a suspension in a binder liquid and subsequently permanentlyconsolidated thereto by heat in an inert environment.

3. Electron emission material comprising a base of molybdenum coatedwith thorium in a coherent and homogeneous state.

4. Electron-emission material comprising afilamentary body with acoating thereon ofa powdered mixture of one of the group of metalsconsisting of thorium, zirconium, uranium, titanium and vanadium as theactive electron-emitter and one of the group of metals consisting ofaluminum, magnesium, chromium and the rare earth metals as a cleanupagent and protector of the active electronemitter.

5. As an article of manufacture, a composite metallic body comprised ofa molybdenum metal base member surfaced at least in part with anadherent, coherent, homogeneous coating of thorium.

In testimony whereof, We have hereunto subscribed our names this 30 dayof July, 1921. v

JOHN WESLEY MARDEN.

HARVEY, CLAYTON RENTSCHLER.

